Here is an example of a good tasting and bad tasting coffee of the same bean. Much in the roast profile are alike, but not all the way. What causes the difference in taste ?
The bean is a high grown washed arabica from Uganda, the Mount Elgon mountain or the border to Kenya.
The good tasting, 400 grams, by Therese
I roasted it again 9 days later. First the the curves were very close. But after 5,5 minutes the ROR levels differed. Here both curves:
The higher ROR level here gave an earlier FC; at 7 minutes in the second roast where as the first had 8:45 min.
This coffee didn’t taste good to me. It had bitterness and burned taste. And not a big aroma.
What could be causing this difference in taste ?
The development-% was around 24% for both (the time after FC related to total roast time). And weightloss was about the same: 14,3 and 14,5%
Development time (DT) was 2:44 minutes for the good one. The bad with more burned taste you would expect to be roasted longer, but no, its roasted a bit shorter: the DT was only 2:19 minutes.
3 possible explanations for the burnt taste
A higher temperature rise in the bad one: 12°Celcius (and BT ended on 181°C) … where as the good one only rose 6-8°C (to end-BT at 175°C).
When entering First Crack the bad one had a ROR around 10°C pr min. Whereas the good one was around 5. The general recommandation is to be at the 5°C level and not as high as 10°C when entering FC and for the rest of the roast.
The amrican roaster Rob Hoos talks about the importance of the middle phase: from yellow point to FC start (see his book “Modulating the flavor profile of coffee“). He calls it the Maillard phase. In these two roasts the drying phase up untill yellow point are not that far apart: 4:00 and 3:45. But the lenght of this middle phase is 3 minutes for the bad one, and 5 minutes for the good one.
Martin Kjeldsen roast of the same bean
Martin Kjeldsen lives in different part of Denmark, but we got the same bean – and the same roaster, the Bullet. The bean is from Uganda from Mount Elgon (on the border to Kenya).
Martin have also roasted the bean several times. This is his best tasting batch:
500 grams, preheat 185°C
Martins bacth was roasted 2 minutes from FC start to end-BT at 192°C. Min good one was roasted 2:45 min and to BT 175°C. But our bean probes do not measure alike. Notice the difference in FC starts. Martin at 182°C. Mine at 167°C and 169°C.
Read more under Roast profiles.